Process for producing cores by microwave heating

ABSTRACT

A process for producing cores in which a core box is formed from a thermosetting resin. A lossy core forming material is inserted into the core box and microwave energy is applied to the core box in a manner which substantially eliminates standing microwaves in the core box.

United States Patent Brown et a1.

[54] PROCESS FOR PRODUCING CORES BY MICROWAVE HEATING [72] Inventors: Lloyd H. Brown, 75 Victor Parkway; Larry C. Stephans, 1044 Abbington Dr., both of Crystal Lake, Ill. 60014 [22] Filed: May 8, 1970 [21] Appl. No.: 35,902

[52] US. Cl. ..i ..l64/15, 164/48, 164/250, 2 l9/10.55 [51] Int. Cl ..B22c 9/12 [58] Field of Search ..l64/37, 43, 48, 50, 250, 14; 219/1055; 156/380 [56] References Cited UNITED STATES PATENTS 2,629,907 3/1953 Hugger ..164/14 2,763,757 9/1956 Pritchard ..219/10.55

[151 3,692,085 51 Sept. 19,1972

3,189,722 6/1965 Fritz ..2l9/10.55

3,259,947 7/1966 Knight ..164/43 3,429,359 2/1969 Hollingsworth 164/37 3,519,517 7/1970 Dench ..219/10.55 X

OTHER PUBLICATIONS The International Dictionary of Physics and Electronics, D. Van Nostrand Company, Inc., 1956. QC 5 15 C12, pg. 986.

Primary Examiner-R. Spencer Annear Attorney-Milton C. Hansen and Donnie Rudd [57] ABSTRACT A process for producing cores in which a core box is formed from a thermosetting resin. A lossy core forming material is inserted into the core box and microwave energy is applied to the core box in a manner which substantially eliminates standing microwaves in the core box.

1 Claim, 2 Drawing Figures MICROWAVE ENERGY PATENTEDSEP I 9 I972 3.692.085

MICROWAVE ENERGY l6 MICROWAVE FIG. 2 W ENERGY 114 l j KM INVENTORSI LL0Y0 H. mow/v LARRY c. YSTEPHA/VS A rmR/vL Y BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to a process for producing cores within acore box wherein the core is cured by the application of microwave energy.

DESCRIPTIONOF THE PRIOR ART One of the major problems of foundry work is providing molds for the articles being cast. The most economical way to provide these molds is to make the mold of as cheap of a material as possible which can withstand the heat of the molten metal for a periodfof time long enough for the molten metal to solidify. After the cast metal has solidified the cast article is removed by the mold being opened. Such structural molds are also necessary when a hollow object is being cast in which the cross-sectional area at some point in'the hollow part is greater than the cross-sectional area at the entranceof the hollow part. It is obvious that in these applications, it is almost necessary to break the core and remove the pieces of the core through the smaller cross-section openings.

The most widely used material for constructing molds and cores in the foundry industry is sand to which has been added a suitable binder material to cause the mold'or core to retain its shape until the material has been poured and solidified. When sand is used in a foundry, the core and moldare formed by a suitable process and the core is placed within the mold and molten metal is poured into the mold. After the metal solidifies the outer mold is broken off and the metal object is usually vibrated to break up the sand so that the sand may be poured out of the openings of the hollow cast object. The sand from the mold and core can then be recovered and reused.

The sand mold is traditionally made from damp sand packed around a model of the object to be cast. The mold is usually made in two halves with the halves being pressed around the opposite halves of the model thereby forming a two piece hollow mold the inner surface of which reproduces the outer surface of the object to be cast.

One of the early ways of making suitable cores was to form a two piece mold the inner surface of which conformed to the outer surface of the core which was desired to be made. Sand mixed with a cereal binder was then pressed or rammed into the mold. The cereal binder held the sand together so that the sand mixture would retain its shape when removed from the mold and then further cured. Such a mold in which a core is made is known in the art as a core box. The core boxes for this application were normally wooden boxes.

The next advance in the foundry art was the so-called no-bake resins where the sand was mixed with a binder v and catalyst and then placed in a wooden box. The

for this'process were normally made of iron or steel and were'made by hand'by skilled die'makers.

Thepresent process is an advancement over all these prior art methods.

-One'of the more recent prior art methods'for'producing cores is explained in U.S. PatfNo. 3,429,359. This method is one in which a core is formed within a core box that is transparent to microwave energy, and the core box is permanently and immovably supported in a microwave heating cavity and the core cured by the application of microwave energy. This process, however, has one serious deficiency in'that it teaches only-the use of a' static, non-moving microwave system. The uneven curing produced by the method does 'not fulfill the needs of the foundry industry. The present invention has overcome these problems associated with the prior art.

SUMMARY OF THE INVENTION It is an object'of this invention to provide a process for producing cores.

It .is another object of this invention to provide a process for producing cores wherein the cores have uniform curing.

It is another object of this invention to provide a systemforproducing cores.

It is still another object of this invention to provide a process for producing core boxes.

It is still a further object of this invention to provide a new and novel core box.

The objects of this invention are accomplished by a processfor producingcores which comprises the steps of forming a core box from a thermosetting resin, preferably coating the interior surface of the core box with a release agent, inserting a lossy core forming material into said core box, and applying microwave energy to said core box in a manner which substantially eliminates standing microwaves in said core box.

More particularly the new process of this invention is one which comprises the steps of forming a core box from a material which is lossless to microwave energy, blowing a lossy core forming material into said core box, and applying microwave energy to said core box in a manner which substantially eliminates standing microwaves in said core box.

The objects of this invention are further achieved by an improvement in the combination of a core box made from a material which is transparent to microwave energy, a microwave heating cavity, means for supporting said core box in said cavity, means for blowing a core forming material into said core box, and means for applying microwave energy to said cavity, wherein the improvement comprises means for eliminating standing microwave in said core box.

In one preferred embodiment of this invention, a core box is formed from a thermosetting resin which is lossless to microwave energy and the core box is then coated with a material which is lossless to microwave energy. This invention includes the coated core box and the method of producing it.

The heart of this new invention lies in the fact that the application of microwave energy to a core box must be in a manner which substantially eliminates standing microwaves in the core box. When microwave energy is introduced in a processing enclosure, some of the microwaves are reflected from the walls of the enclosure. These reflected microwaves reenforce each other in some locations in the enclosure and cancel each other out in other locations in the enclosure. When an object is being heated in the enclosure, the reenforced waves cause hot spots, and the wave-canceled locations cause cold spots in the object. By the term standing microwaves it is therefore intended to mean reflected microwaves which reenforce and cancel each other out causing hot and cold spots in the object to be heated.

One method of eliminating standing microwaves in a core box is to design the enclosure and the core box so that the microwaves will not substantially reenforce or cancel each other. This presents some design problems, however, and is thus not the preferred practice in foundry operations.

The preferred method of eliminating standing microwaves in the core box is to apply the microwave energy to the core box as the core box moves through or past the microwave energy source. One method of accomplishing this is to have the core box travel on a conveyor through a microwave oven. The heating accomplished by this process is a result of many different combinations of reenforced and canceled microwaves, the sum total of which results in even heating and curing of the core in the core box.

By use of the term thermosetting resin it is intended to mean generally a resin which sets or polymerizes upon heating. Of particular importance to this invention are polyurethanes of the non-elastomeric type which are also lossless to microwave energy. Also of importance in this invention are furfuryl alcohol resins or furan resins consisting of polymerized furfuryl alcohol. In these resins, further polymerization to a solid from the normally liquid resin can be accomplished by the addition of a catalyst. When the furan resins are used as core binders in microwave applications, the resin may contain a lossy material such as urea. When the resins are used as binder for the core box, an essentially un-modif1ed furfuryl alcohol resin can be used since the cured resin must be substantially transparent to microwave energy. At this point, it is important to note that furfuryl alcohol monomer and slightly polymerized furfuryl alcohol are lossy to microwaves while substantially polymerized furfuryl alcohol is substantially lossless to microwaves. As a furfuryl alcohol monomer is cured to form a polymer, it necessarily changes from a lossy material to a lossless material. Also of particular importance for use in this invention are the phenolic resins consisting of phenol and some other material such as formaldehyde and providing that the combination is lossy to microwave energy when the resin is used as a core binder and providing that the resin is lossless to microwave energy when it is used as a binder for the core box.

Of special importance as a preferred embodiment of this invention is a foundry core composition prepared by the process comprising the steps of:

a. forming a monomeric binder mixture of from 2 to 10 percent weight of aqueous urea formaldehyde mixture, from 0.0125 to 0.5 percent by weight gamma amino propyl triethoxy silane, and from 89.5 to 97.9875, percent by weight furfuryl alcohol, said aqueous area formaldehyde mixture containing from about 5 to about 25 percent by weight water;

b. forming a mixture of from 3,700 to 3,979parts by weight sand and from 1 to 100 parts by weight acidic catalyst; and

. admixing from k to 5 percent by weight of the monomeric binder with from to 99.5 percent by weight of the sand-acidic catalyst mixture. The definition of the terms urea formaldehyde mixture and acidic catalyst and other procedure may be taken to be the same as is defined in US. Pat. No. 3,168,489 to Lloyd H. Brown et al. issued on Feb. 2, 1965, with the notable difference in the stated amount of water in the urea-formaldehyde mixture.

One embodiment of this invention is the process for producing cores which comprises the steps of forming a core box from a thermosetting resin, coating the interior surface of said core box with a material which is lossless to microwave energy, inserting a lossy core forming material into said core box, and applying microwave energy to said core box in a manner which substantially eliminates standing microwaves in said core box. The forming of the core box from a thermosetting resin is accomplished by methods well known to the art. The resins used in forming the core box comprise the hereinbefore mentioned furfuryl alcohol resins or furan resins, phenolic resins, polyurethanes and mixtures thereof. It is preferred to coat the interior surface of the core box with a material which will decrease the bonding between the resin in the core mix and the core box. Any suitable material may be used for coating the interior surface of the core box as long as the material has properties which allow it to be applied in a coating form. The coating material or release agent can be substantially lossless to microwave energy. It is to be understood, however, that in some applications it may be desired to provide a quicker cure or higher degree of cure at the surface of the core in which case a lossy material should be added to the coating material to achieve the desired result. Among the substantially lossless materials that may be used for coating the interior surface of the core box are the various polymers such as polyethylene, polypropylene, and polyurethane either alone or in some type of solution. Other plastic materials which are lossless to microwave energy should be equally acceptable for this coating procedure. The lossy core forming material that is then inserted into the core box comprises one of the aforementioned furfuryl alcohol or furan resins, phenolic resins, or polyurethanes each of which has had added thereto a lossy material. When phenolic resins are used as the core binder, formaldehyde is the most frequently preferred lossy material to be added to the resin. These lossy materials are not the only ones that are operable, however, and other well known lossy materials common to the microwave art such as ferrite materials or carbon may also be added to the resins to impart a lossy nature to them. The resin with the lossy material therein is then cured by the application of microwave energy to the core box in a manner which substantially eliminates standing microwaves in the core box.

This invention also includes a process for making cores which comprises the steps of forming a core box from a material which is lossless to microwave energy, blowing a lossy core forming material into the core box and applying microwave energy to the core box in a manner which substantially eliminates standing microwaves in the core box. Once more it is emphasized that the elimination of standing microwaves in the core; box is an achievement ment which the prior art has never obtained in foundry art.

The prior art has disclosed a core box made from a material which is transparent to microwave energy, a microwave heating cavity, means for supporting the core box in the cavity, means for blowing a core forming material into the core box, and means for applying microwave energy to the cavity. This invention, however, includes the improvement in the above described prior art wherein the improvement comprises the addition of means for eliminating standing microwaves in the core box. The preferred embodiment of this improvement is one in which the means for blowing a core forming material into the core box is a means for blowing a mixture of sand and a thermosetting resin into the core box wherein the thermosetting resin is the same as has previously been described.

This invention also includes a new and novel core box comprising a formed thermosetting resin coated with a material-which is lossless to microwave energy wherein said thermosetting resin is also substantially lossless to microwave energy. The formed thermosetting resin for this core box is the same as has hereinbefore been described with care being taken to insure that-no material is included which is lossy to microwave energy. Likewise, the coating materials that are herein used are those which have hereinbefore been described such as polyethylene, polypropylene, polyurethane, etc.

The new process for producing these core boxes comprises the steps of forming a core box from a thermosetting resin which is lossless to microwave energy and then coating the core box with a material which is substantially lossless to microwave energy. Again the terms used herein are those which have hereinbefore been described.

BRIEF DESCRIPTION OF THE DRAWING The objects of this invention are accomplished as illustrated in the accompanying drawings in which:

FIG. 1 is a side view of the apparatus used to perform the process of our invention; and

FIG. 2 is a top view thereof.

In the drawings, I have used the numeral 11 to illustrate a conveyor belt passing over drive means 12 and 13. Core boxes 14 are placed on the conveyor to pass through the microwave energy source. A microwave cavity 15 surrounds a portion of the conveyor and is supplied by microwave energy from source 16 through transmitters 17 and 18 located on the exterior of the cavity.

In operation, the core boxes are placed on the conveyor belt which is set in motion. The speed of the conveyor belt determines the exposure to the microwave energy. The microwave energy is set to provide the amount of microwave energy desired in the microwave cavity. As the core boxes pass through the microwave cavity, the cores are cured.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples may be taken to constitute preferred embodiments of this invention.

EXAMPLE 1 A sand mix was prepared by thoroughly admixing 90 weight percent sand,l0 weight percent silica flour and 10 weight percent clay. Ten weight percent (based on sand weight) of.a no-bake furan resin (greater than 50 percent by weight furfuryl alcohol, Steelset trademark, Aristo Corp.Intemational Minerals & Chemical Corp.) was then mixed with the sand mix and 15 weight percent (based on resin weight) of concentrated phosphoric acid was then added and mixed therein. A wooden model was prepared and placed in a wooden mold. Both the model and mold were coated with coating material comprising about 53.5 percent water, 3.5 percent Western bentonite, 24 percent graphite, 6 percent sodium soap of coconut oil, and 13 percent methanol. The sand-resin mixture was then packed lightly around the coated model in the mold. The wooden mold was used to hold the sand-resin mixture until the resin cured. A thin plastic sheet (a polyethylene terephtahalate, Mylar, E. I. du Pont de Nemours & Co., Wilmington, Del.) was fastened to the mold to divide the mold into two parts at the core cavity. After the resin was cured, the plastic sheet was unfastened from the mold and the core box removed from the mold. The box was easily splitat the plastic sheet and the core model removed. Since vents were not molded into the core box, they were then drilled in the box. The core cavity was then coated with a thin film of polyurethane. A sand mix consisting of about 50 weight percent reclaimed sand (containing about 1.7 weight percent carbonaceous material) and 50 weight percent foundry sand were mixed with 2 weight percent (based on total sand weight) of a furan hot box binder (furfuryl alcohol resin, Sanset 22, trademark, Aristo Corp.Intemational Minerals & Chemical Corp.) catalyzed with 20 weight percent aqueousammonium chloride: urea catalyst (Sanset 2, trademark of Aristo Corp.Intemational Minerals & Chemical Corp.). After the sand, resin, and catalyst were thoroughly mixed, the mixture was blown into the core cavity. The sand core box containing the uncured core was then passed into a microwave cavity on a conveyor belt and exposed to 3,000 watts of microwave power at 2,450 megacycles per second for 30 seconds. The core box was kept moving at approximately the same speed during its entire 30 second exposure in the microwave cavity. After the exposure period, the core box was moved out of the microwave cavity and after 3 minutes at room conditions, the core was stripped from the core box. The core was found to exhibit properties superior to any produced by prior microwave treatments.

EXAMPLE 2 Example 1 was repeated except the no-bake furan resin comprised 92 parts by weight furfuryl alcohol, 8 parts by weight urea-formaldehyde concentrate, and 0.1 parts by weight gamma amino pro pyl triethoxy silane. This core was also found to exhibit properties superior to any produced by prior microwave treatments.

EXAMPLE 3 A quantity of silica sand was weighed and set aside. A quantity of no-bake furan resin (greater than 50 weight percent furfuryl alcohol, Steelset trademark,

Aristo Corp.lnternational Minerals & Chemical Corp.) equal to 12.5 percent by weight based on the weight of the sand was then weighed and set aside. Next, 15 weight percent (based on furan resin weight) of a 70 percent solution of para toluene sulfonic acid in water was thoroughly mixed with the sand. The furan resin was then thoroughly mixed with the sand-catalyst mixture. After thorough mixing, the sand-resin-catalyst mixture was packed in a polyethylene mold around a polypropylene model of the core. The mold containing the uncured sand-resin-catalyst mixture was then passed into microwave cavity on a conveyor belt and exposed to 3,000 watts of microwave power at 2,450 megacycles per second for 90 seconds. The mold and its contents were kept moving at approximately the same speed during the entire 90 second exposure. After removal from the microwave cavity, the mold was allowed to set at room conditions for 3 minutes and the core box was then removed from the mold and the core model removed from the core cavity. The core was then brushed with a solution of water-bentonite-graphite-soap-methanol (same as in Example 1). Vent holes were then drilled in the core box to permit use of a conventional core blower to blow the core mix into the core cavity. Enough sand to fill the core cavity was then weighed and mixed with 2 weight percent (based on sand weight) of a no-bake furan resin (furfuryl alcohol) and 20 weight percent (based on resin weight) of concentrated phosphoric acid, the acid being mixed with the sand first and then followed by the resin. The core mix was then blown into the core cavity and the core box containing the uncured core mix was passed into the microwave cavity and exposed to 3,000 watts of microwave power at 2,450 megacycles per second for 30 seconds. The core box was kept moving in the microwave cavity at approximately the same speed during the 30 second exposure. After the core box was removed from the microwave cavity, the core was immediately stripped from the core box. Again the core was found to exhibit excellant properties.

EXAMPLE 4 A quantity of foundry sand was weighed and set aside. An amount of greater than 90 percent furfuryl alcohol containing no-bake resin equal to 15 percent by weight of the sand was then weighed and set aside. A solution of sulphuric acid (50 percent sulphuric acid in water) equal to percent by weight of the furan resin was then mixed with the sand, and the resin binder was then mixed with the sand and catalyst. After thorough mixing, the sand-resin-catalyst mixture was packed in a metal mold which had been coated with the waterbentonite-graphite-soap-methanol mixture described water-bentonite-graphite-soap-methanol Example 1. The mold contained in a wooden core model also coated with the same mixture. The mixture was allowed to cure and after curing the core box was removed from the mold and the core model removed from the core cavity. Vent holes were drilled in the core box to permit use on a conventional core blowing machine. The core cavity surface was then coated with silicone release agent. Enough sand to fill the core cavity was then weighed and to it was added about 1 percent'by weight powdered graphite. Two percent (based on sand wei t) of a henolic resin binder Sanset 33 trademar Arrsto orp.--lnternational merals & Chemical Corp.) and 20 weight percent (based on phenolic resin weight) of aqueous ammonium chloride: urea catalyst were then mixed with the sand to form a core mix. The core mix was then blown into the core cavity with a, conventional core blower. The core box was then placed on a conveyor belt and passed through a microwave cavity where it was exposed to 3,000 watts of microwave power at 2,450 megacycles per second for 60 seconds. The core box was kept moving at approximately a constant speed during the exposure. After the core box was removed from the microwave cavity, it was allowed to set for about 3 minutes at room conditions, and the core was then stripped from the core box.

In each of the above examples, the boxes where able to be subjected to at least core blowing-core forming sequences without exhibiting a wear of over 0.005 inches. This was superior to anything produced by prior microwave art.

Having fully described this new and novel invention, we claim:

1. In a process for producing cores which comprises the steps of forming a core box from a thermosetting resin and inserting a lossy core forming material into said core box, the improvement comprising coating the interior surface of the core box with a release agent which is substantially lossless to microwave energy and then after inserting the lossy core forming material'into the core box, applying microwave energy to said core box in a manner which substantially eliminates standing microwaves in said core box by continuously moving the core box through the microwave energy until the core is cured. 

1. In a process for producing cores which comprises the steps of forming a core box from a thermosetting resin and inserting a lossy core forming material into said core box, the improvement comprising coating the interior surface of the core box with a release agent which is substantially lossless to microwave energy and then after inserting the lossy core forming material into the core box, applying microwave energy to said core box in a manner which substantially eliminates standing microwaves in said core box by continuously moving the core box through the microwave energy until the core is cured. 